Polycystic ovary syndrome (PCOS) is the most common cause of female infertility due to anovulation in the United States, and insulin resistance with compensatory hyperinsulinemia plays a central role in its pathophysiology. Lifestyle measures, including diet and weight loss, are frequently considered as first-line management for improving reproductive outcomes in PCOS. Although weight loss has proven beneficial in restoring ovulatory function, the optimal dietary composition for improving ovulation in PCOS remains unclear. Understanding the optimal diet for improving reproductive function in women with PCOS would greatly enhance infertility management for PCOS, but to date few studies have examined the role of dietary composition on reproductive abnormalities in PCOS. Strong evidence suggests that high dietary fiber ngestion can improve insulin sensitivity although no published studies have investigated the effect of high fiber intake on ovulation rates in women with PCOS. The average total daily dietary fiber intake in Americans is less than 14 g, much less than the recommended 20 to 35 g/day. Studies have shown that intakes of 28- 36 g fiber/day, consisting of both soluble and insoluble fiber, improve insulin sensitivity and reduce circulating insulin in adults. We hypothesize that 6 months of fiber supplementation will improve ovulation in premenopausal women with PCOS, independent of weight loss. In this pilot study, we will determine the feasibility of conducting a larger double-blind, randomized trial in women with PCOS to test this hypothesis. Therefore, we will evaluate 15 women with PCOS between ages 18 to 45 years (body mass index <45 kg/m2)to identify the effect of adding up to 22 g/day of fiber supplementation to their usual weightmaintenance diets on ovulation. Fiber supplementation, as opposed to change in dietary fiber intake, could feasibly be translated into clinical practice. Specifically, we will: 1) Generate preliminary data on the range of outcome measures at baseline and after 6 months of fiber supplementation on: ovulation rates, as measured by urinary pregnanediol-3-glucuronide measurements;insulin sensitivity, as measured by frequently sampled intravenous glucose tolerance testing;concentrations of circulating androgens, estradiol, sex-hormone binding globulin, and luteinizing hormone;and satiety, as measured by a visual analog scale;2) Quantify enrollment strategies, retention, compliance, participant characteristics, and data collection challenges;3) Determine whether a dose of up to 22 grams of liquid fiber supplementation would be tolerable and sufficient to affect ovulation rates and insulin sensitivity in women with PCOS.;and 4) Determine whether 6-month duration of fiber supplementation is sufficient to affect ovulation rates and insulin sensitivity in women with PCOS.